module speed_select(clk,rst_n,bps_start,clk_bps);

input clk; // 50MHz主時鐘
input rst_n;  //低電平復(fù)位信號
input bps_start;  //接收到數(shù)據(jù)后，波特率時鐘啟動信號置位
output clk_bps;   // clk_bps的高電平為接收或者發(fā)送數(shù)據(jù)位的中間采樣點 

parameter 		bps9600       = 5207,    //波特率為9600bps
				bps19200   = 2603,    //波特率為19200bps
				bps38400   = 1301,    //波特率為38400bps
				bps57600   = 867, //波特率為57600bps
				bps115200  = 433; //波特率為115200bps

parameter 		bps9600_2 = 2603,
				bps19200_2 = 1301,
				bps38400_2 = 650,
				bps57600_2 = 433,
				bps115200_2 = 216;  

	reg[12:0] bps_para;  //分頻計數(shù)最大值
	reg[12:0] bps_para_2;    //分頻計數(shù)的一半
	reg[12:0] cnt;           //分頻計數(shù)
	reg clk_bps_r;           //波特率時鐘寄存器

 

//----------------------------------------------------------
			reg[2:0] uart_ctrl;  // uart波特率選擇寄存器
//----------------------------------------------------------

 always @ (posedge clk or negedge rst_n) begin
    if(!rst_n) begin 
           uart_ctrl <= 3'd0;   //默認(rèn)波特率為9600bps
       end
    else begin
           case (uart_ctrl)  //波特率設(shè)置
              3'd0:  begin
                     bps_para <= bps9600;
                     bps_para_2 <= bps9600_2;
                     end
              3'd1:  begin
                     bps_para <= bps19200;
                     bps_para_2 <= bps19200_2;
                     end

              3'd2:  begin
                     bps_para <= bps38400;
                     bps_para_2 <= bps38400_2;
                     end

              3'd3:  begin
                     bps_para <= bps57600;
                     bps_para_2 <= bps57600_2;
                     end

              3'd4:  begin
                     bps_para <= bps115200;
                     bps_para_2 <= bps115200_2;
                     end

             default: ;
              endcase
       end
end

 
always @ (posedge clk or negedge rst_n)

    if(!rst_n) cnt <= 13'd0;
    else if(cnt<bps_para && bps_start) cnt <= cnt+1'b1;  //波特率時鐘計數(shù)啟動
    else cnt <= 13'd0;

always @ (posedge clk or negedge rst_n)

    if(!rst_n) clk_bps_r <= 1'b0;
    else if(cnt==bps_para_2 && bps_start) clk_bps_r <= 1'b1;    // clk_bps_r高電平為接收或者發(fā)送數(shù)據(jù)位的中間采樣點 
    else clk_bps_r <= 1'b0;

assign clk_bps = clk_bps_r;
endmodule